Lithium/CrO.sub.x cells of the general type mentioned above are known from German Patent DE No. 24 26 380. In the commercially available embodiment as a cylindrical cell such a cell comprises a pair of CrO.sub.x rings pressed into a nickel-plated steel cup, having a diameter of 14.8 millimeters and a height of 50.5 millimeters. The remaining cylindrical volume comprises a lithium rope provided with a peg takeoff surrounded by a separator sheath. The separator further encloses the electrolyte which, conventionally, is a mixture of propylene carbonate and dimethoxyethane in which lithium perchlorate is dissolved as the conductive agent.
The are of utility of the invention is not limited to the aforementioned type of cell but includes other lithium organic systems with metal oxide cathodes for example, which contains only a portion of CrO.sub.x and which are made substantially of manganese dioxide, silver monoxide, disilver oxide, or nickel hydroxide. The CrO.sub.x may be provided as a coating layer pressed on to a carrier base of the aforesaid metal oxides.
The compact construction of the active components in such a cell emphasizes not only the desired properties provided by the separator such as assurance against short circuits between the electrodes, but equally, certain disadvantages are also emphasized. Thus, in view of the ultimate resistance value of the separator, there is provided a barrier to the passage of an ionic current which thus reduces the capacity of the cell. In order to overcome these problems, provision must be made for increasing the porosity of the separator which in turn increases the cost factor for this component. Furthermore, because of the rather tight space constraints between string-formed lithium anode and the ring cathode, the separator can interfere in the necessary exchange between electrolyte and gas bubbles which occasionally leads to disruptions during the discharge of the cell.
It is known that it is not always unequivocally necessary to prevent all direct contact between an anode and the cathode depolarizer in an electrochemical cell, since certain cathodic substances, at least in the preferred circuit, do not necessarily enter into a chemical reaction with an adjacent active metal anode. In such instances, it is noted that the metal anode is caused to be merely covered by a thin film comprising an insoluble reaction product between the anode and the cathode, said film being of unspecified composition, which on the one hand does not exceed the thickness of a passivating film, but on the other hand, does not substantially effect the chargeability or dischargeability of the anodic metal.
A lithium cell of this type utilizing sulfur dioxide as the cathode depolarizer in which, for reasons similar to those set forth above, a conventional separator may be omitted, is disclosed in U.S. Pat. No. 3,567,515. In this case the upper surface of the lithium is converted into a sheath of lithium dithionite as a discharge product, which takes on the separator function.
In accordance with U.S. Pat. No. 3,926,669, lithium is also noted to be stable in an electrochemical cell wherein oxyhalides and thiohalides, in particular thionyl chloride are utilized as depolarizing agents. It is further disclosed in U.S. Pat. No. 4,049,890 that in a lithium iodide solid phase cell the separator is created in situ from an ion conductive lithium iodide interface, which at the same time serves as the electrolyte.
It would therefore be desirable to formulate a galvanic primary element of the lithium/CrO.sub.x type in which the disadvantages associated with conventional separators made out of polypropylene or paper can be substantially avoided.